1. Field of the Invention
This invention relates generally to hot rolling mills of the type producing bar and rod products, and is concerned in particular with improvements in the pinch roll units and associated controls employed to propel and/or retard the movement of such products at various places along the mill pass line.
2. The Prior Art
Pinch roll units are conventionally employed in rod mills to propel smaller diameter products through water boxes, and to propel larger diameter products through the laying heads. Alternatively, pinch roll units can be employed to retard and brake the movement of bar products being directed to cooling beds, and to prevent the tail ends of rod products from accelerating after they leave the last mill stand and before they arrive at the laying heads.
Pinch roll closure must be precisely timed to achieve the desired function, and the pinching force and torque exerted by the pinch rolls must be carefully controlled and coordinated to avoid marking the product. Marking can result from excessive pinching force, or by an imbalance of pinching force and driving torque resulting in slippage of the rolls against the product surface.
Conventional pinch roll units employ electric motors to drive the pinch rolls, and pneumatically driven linear actuators to open and close the pinch rolls. The latter have proven to be problematical due to fluctuations in the pressure of compressed air normally available in rolling mills, and the relatively slow reaction times attributable largely to solenoid valve dead times, cylinder closing times, and the stroke distance of the pistons. Such problems are particularly acute in high speed rolling environments, e.g., in rod mills where product delivery speeds now routinely exceed 100 m/sec.
The principal objective of the present invention is to eliminate or at least significantly minimize the above described problems by replacing the conventional pneumatically driven linear actuators with more reliable faster acting electrically driven closure mechanisms.